Heterostructured Pt-Ni_(3)Mo_(3)N formed via ammonia-containing polyoxometalates for highly efficient electrocatalytic hydrogen evolution in acid medium

Constructing heterostructured nanohybrid is considered as a prominent route to fabricate alternative electrocatalysts to commercial Pt/C for hydrogen evolution reaction(HER).In this work,(NH_(4))_(4)[NiH_(6)Mo_(6)O_(4)]·5H_(2)O polyoxometalates(NiMo_(6))are adopted as the cluster precursors for simple fabrication of heterostructured Pt-Ni_(3)Mo_(3)N nanohybrids supported by carbon black(Pt-Ni_(3)Mo_(3)N/C)without using additional N sources.The improved porosity and enhanced electronic interaction of Pt-Ni_(3)Mo_(3)N/C should be attributed to the integration of Pt with NiMo_(6),which favors the mass transport,promotes the formation of exposed catalytic sites,and benefits the regulation of intrinsic activity.Thus,the as-obtained Pt-Ni_(3)Mo_(3)N/C exhibits impressive and durable HER performance as indicated by the low overpotential of 13.7 mV at the current density of 10 mA cm^(-2) and the stable overpotential during continuous working at 100 mA cm^(-2) for 100 h.This work provides significant insights for the synthesis of new highly active heterostructured electrocatalysts for renewable energy devices.

Polyoxometalates-engineered hydrogen generation rate and durability of Pt/CNT catalysts from ammonia borane

Heterogeneously catalyzed hydrolytic dehydrogenation of ammonia borane is a remarkable structure sensitive reaction. In this work, a strategy by using polyoxometalates(POMs) as the ligands is proposed to engineer the surface and electronic properties of Pt/CNT catalysts toward the enhanced hydrogen generation rate and durability. Three kinds of POMs, i.e., silicotungstic acid(STA), phosphotungstic acid(PTA)and molybdophosphoric acid(PMA), are comparatively studied, among which the STA shows positive effects on the catalytic activity and durability. A catalyst structure-performance relationship is established by a combination of kinetic and isotopic analyses with multiple characterization techniques, such as HAADF-STEM, EDS, Raman spectroscopy and XPS. It is shown that the STA compared to the other two POMs can increase the Pt binding energy and thus promote the reaction. The insights demonstrated here could open a new avenue for boosting the reaction by employing the POMs as the ligands to engineer the catalyst electronic properties.

Study on photodegradation of Azo dye by polyoxometalates/polyvinyl alcohol

A series of photocatalysts, K11[Ln(PW11O39)2]/PVA (Ln=La, Ce, Pr, Nd, Sm) were prepared by K11[Ln(PW11O39)2] (Ln=La, Ce, Pr, Nd, Sm) containing five kinds of lanthanides and polyvinyl alcohol as the support. The catalysts obtained were characterized by Fourier transform infrared spectra, UV-vis spectra, powder X-ray diffraction, and scanning electron microscopy, indicating that the structure of K11[Ln(PW11O39)2] and polyvinyl alcohol remained intact, respectively. The photocatalysts exhibited efficient catalytic activity to degrade methyl orange, Congo Red, Ponceau 2R. The maximal degradation conversions of the three kinds of dyes were 99.58%, 47.61%, 72.42%, respectively.

Hybrid Self-Assembled Multilayer Films Formed by Alternating Layers of Keggin Polyoxometalates and 1,10DAD

Hybrid self-assembled multilayer films were prepared by alternate adsorption of 1,10-diaminodecane (1,10-DAD) and Keggin polyoxometalates of SiW12O404-, SiW11VO405-, and PMo12O403-, respectively. The films were reproducibly grown at each adsorption cycle as monitored by UV spectroscopy.

Hydrothermal Synthesis and Structural Characterization of two Hybrid Keggin-based Polyoxometalates

Two new hybrid polyoxotungstates, [Co（2,2＇-bipy）3][a-H5PW11CoO40]-3H2O 1 and [Fe（2,2＇-bipy）3]2[a-HBW12O40]-2.5H2O 2 （2,2＇-bipy = 2,2＇-dipyridyl）, have been hydrothermally synthesized and characterized by IR, TGA and single-crystal X-ray structural analyses. The results of X-ray crystallography analyses exhibit that 1 consists of one a-Keggin anion [a-H5PW11CoO40]2- and one isolated [Co（2,2＇-bipy）3]2＋ complex, while 2 is constructed from one a-Keggin anion [a- HBW12O40]4- and two isolated [Fe（2,2＇-bipy）3]2＋ cations. The data for 1： orthorhombic system, space group Pbcn, a = 16.062（6）, b = 27.278（10）, c = 16.951（6）A, V = 7427（5）A3 and Z = 4; and those for 2： triclinic system, space group P1, a = 13.787（3）, b = 17.857（5）, c = 18.918（5）A, a = 88.009（12）, β = 72.768（10）, γ = 74.935（10）°, V = 4291（2）A3 and Z = 2.

Kinetics of Photocatalytic Degradation of Formic Acid over Silica Composite Films Based on Polyoxometalates

The composite films, XW11O39n-/SiO2, (X refers to Si, Ge or P, respectively) were prepared by tetraethoxysilane (TEOS) hydrolysis sol-gel method via spin-coating technique. Formation of the composite films is due to strong chemical reaction of organic silanol group with the surface oxygen atoms of XW11O39n-, resulted in the saturation of the surface of the lacunary polyoxometalates (POMs). Therefore, the coordination structural model of the films was proposed. As for the films, retention of the primary Keggin structure was confirmed by UV-vis, FT-IR spectra and MAS NMR. The surface morphology of the films was characterized by SEM, indicating that the film surface is relatively uniform, and the layer thickness is in the range of 250~350 nm. Aqueous formic acid (FA) (0-20 mmol/L) was degraded into CO2 and H2O by irradiating the films in the near-UV area. The results show that all the films have photocatalytic activities and the degradation reaction follows Langmuir-Hinshelwood first order kinetics.

Polyoxometalates Pillared Hydrotalcite:Synthesis and Catalysis in Transesterification of Dimethyl Carbonate and Phenol

The salts of para-tungstic and para-molybdic were heterogenized for their effective use as solid catalysts in the transesterification reaction of dimethyl carbonate and phenol by inserting them between the layers of Mg2Al-hydrotalcite. These catalysts were characterized by FT-IR spectra and X-ray powder diffraction. Polyoxometalates （POMs） clusters were intercalated into the interlayer of layered double hydroxide （LDH） via anion exchange with organic acid precursor in Mg2Al-LDH, and the integrity of the clusters [W7O24 ]^6- and [Mo7O24 ]^6- was maintained. The intercalated para-molybdic cluster showed high catalytic activity and reusability in the transesterification under mild reaction conditions. When the reaction was carried out at 180 ℃, with a molar ratio of phenol to DMC of 1 ： 1, a reaction time 10 h, and a catalyst amount 1% （wt）, the conversion of phenol was 10.0 %, the selectivities of diphenyl carbonate and methyl phenyl carbonate were 10.7 % and 86.1%, respectively.

Synthesis,Characterization and Catalytic Activity of Polyoxometalates Derived from α-P2W15O56(12

Ｓｙｎｔｈｅｓｉｓ，ＣｈａｒａｃｔｅｒｉｚａｔｉｏｎａｎｄＣａｔａｌｙｔｉｃＡｃｔｉｖｉｔｙｏｆＰｏｌｙｏｘｏｍｅｔａｌａｔｅｓＤｅｒｉｖｅｄｆｒｏｍα－Ｐ;Ｗ;Ｏ;６;ＬｉｇａｎｄＭＥＮＧＬｕ，ａｎｄＬＩＵＪｉｎｇ－ｆｕ(Ｄｅｐａ...

Electrochemical-reduction-assisted Assembly of Pd NPs/Polyoxometalates/Graphene Ternary Nanocomposite and Its Electrocatalytic Performance toward Formic Acid Oxidation

A novel ternary nanocomposite, Pd nanoparticles（NPs）/polyoxometalates（POMs）/reduced graphene oxide（rGO）, was prepared by a green, mild, electrochemical-reductionassisted assembly. It is worth noting that the Keggin-type POM acts as an electrocatalyst as well as a bridging molecule. During the reduction process, POMs transfer the electrons from the electrode to GO, leading to a deep reduction of GO and the content of oxygen-containing groups is decreased to around 6.1%. Meanwhile, the strong adsorption effect between the POM clusters and rGO nanosheets induces the spontaneous assembly of POM on r GO in a uniformly dispersed state, forming a nanocomposite. The ternary Pd NPs/POMs/rGO nanocomposite exhibits higher electrocatalytic activities, better electrochemical stability, and higher resistance to CO poisoning than the Pd/C catalyst towards the formic acid oxidation（FAOR）. Especially, the Pd/PW（12）/rGO exhibits the best electrocatalytic performance among three Pd/POMs/rGO composites（POMs = PW（12）, SiW（12）, PMo（12））.

Study of Safety of Molybdenum and Iron-Molybdenum Nanoclaster Polyoxometalates Intended for Targeted Delivery of Drugs

Nanocluster polyoxometalates with a structure of buckyball (fullerene) are a promising means of targeted delivery of drugs in the body. In this paper, based on an analysis of histological sections of liver and kidney and peripheral blood, showed a significant reduction of toxicity of buckyballs, containing ions of molybdenum (VI), the substitution of Mo (V) ions to Fe (III), in contrast to buckyballs based on Mo (V). The absence of accumulation of molybdenum in rats with a daily intramuscular injection of aqueous solutions of both drugs within a month was confirmed.

Assembly and Electrochemical Study of Transition Metal Substituted Polyoxometalates SiW_(11)NiO_(39)^(6-) and SiW_(11)MnO_(39)^(6-) on 4-Aminothio-phenol Modified Glassy Carbon Electrode

Via layer-by-layer assembly, the polyoxometalates of Keggin type, SiW_ 11O_ 39Ni(H_2O) 6-(SiNiW_ 11) and {SiW_ 11O_ 39Mn(H_2O) 6-}(SiMnW_ 11) were first immobilized on a 4-aminothiophenol(4-ATP) modified glassy carbon electrode surface. The electrochemical behavior of these polyoxometalates was investigated. They exhibited some special properties in the films, which are different from those in a homogeneous aqueous solution. Their reaction mechanism in a multilayer film is proposed. The electrocatalytic behavior of these multilayer film electrodes for the reduction of BrO-_3 and NO-_2 were comparatively studied.

Effects of Cs-substitution and partial reduction on catalytic performance of Keggin-type phosphomolybdic polyoxometalates for selective oxidation of isobutane

The catalytic performance of Cs-substituted phosphomolybdic salts was studied for selective oxidation of isobutane. The results of activity tests revealed that 360 °C was the optimal reaction temperature. It was demonstrated that oxidizing sites not only took dominating part in the activation of isobutane, but also influenced the product distribution. Besides, appropriate Cs addition led to moderate acidity of catalysts, favoring the selectivity to desired products. Furthermore, to obtain partially reduced catalysts, different calcination atmospheres were investigated and certain proportion of Mo^（5＋） produced during calcination was crucial for the redox reaction. The catalyst calcined in N2 showed the highest yield of MAA（7.0%）. Fe-substitution enhanced the activity of catalysts by rapid reoxidation of Mo^（5＋）.

Functionalization of carbon nanotubes/graphene by polyoxometalates and their enhanced photo-electrical catalysis

Carbon nanotubes and graphene are carbon-based materials, which possess not only unique structure but also prop- erties such as high surface area, extraordinary mechanical properties, high electronic conductivity, and chemical stability. Thus, they have been regarded as an important material, especially for exploring a variety of complex catalysts. Considerable efforts have been made to functionalize and fabricate carbon-based composites with metal nanoparticles. In this review, we summarize the recent progress of our research on the decoration of carbon nanotubes/graphene with metal nanoparticles by using polyoxometalates as key agents, and their enhanced photo-electrical catalytic activities in various catalytic reactions. The polyoxometalates play a key role in constructing the nanohybrids and contributing to their photo-electrical catalytic properties.

Studies on Model Interaction of Keggin-type Polyoxometalates with Nucleic Acid

Keggin anions behave differently from each other when they react with nucleic acids. The molybdenum series exhibits oxidative cleavage activity towards AMP and DNA. The mechanism of AMP damage and DNA cleavage caused by the molybdenum series is mainly oxidation and the oxidation sites are on the ribose parts other than on the adenine parts, while the hydrolysis probably makes significant contributions to the cleavage of DNA and to the damage of AMP caused by the tungsten series.

Synthesis and Characterization of Two New Photochromic Inorganic-organic Hybrid Materials Based on Keggin-type Polyoxometalates

Two new photochromic inorganic-organic hybrid materials formed from Keggin-type polyoxometalates（POMs） and metronidazole （C6H9N3O3, MNZ）, formulated as H3PMo12OaO-3MNZ·3H2O （1） and H3PW12O40.3MNZ·3H2O（2）, were synthesized and characterized by elemental analysis, IR spectra, electronic spectra, electron spin resonance （ESR） spectra and thermogravi-metry-differential thermal analysis （TG-DTA）. Reflectance spectra show the presence of weak intermolecular charge transfer between the organic and inorganic moieties in the solid state. The photochromic properties were studied by solid diffuse reflectance spectra and ESR spectra, and the photochromic reactions were found to exhibit first-order kinetics. TG-DTA showed that two hybrid materials have similar thermal behavior.

Three New Polyoxometalates Derivatives Decorated by Phenanthroline and Transition-metal Cations(M=Zn~ⅡI , Co~Ⅱ , Ni~Ⅱ)

Three new Keggin polyoxometalates, [Zn（phen）3]2[SiW12O40]＇5H2O（1）, [Co（phen）3]2[SiW12O40]（2） and [Ni（phen）3]2[SiW12O40].2H2O（3）（phen=1,10＇-phenanthroline） have been hydrothermally synthesized and characterized by elemental analysis, IR, crystal X-ray diffraction, thermogravimetric analyses（TGA） and fluorescence tech- niques. Complex 1, crystallized in the triclinic space group Pi, consists of one [SiW12O40]4 anion, two discrete [Zn（phen）3]^2＋ cations and five crystal water molecules. Complexes 2 and 3 have the similar configuration to complex 1, but they crystallized in the monoclinic space group C2/c. Variable-temperature magnetic susceptibilities of complexess 2 and 3 reveal antiferromagnetism and ferromagnetism, respectively.

Anti-HepG-2 Cell Properties of Rare Earth TungstosilicicPolyoxometalates Containing 5-Fluorouracil

Two novel rare earth tungstosilicic polyoxometalate containing 5-fluorouracil,K26(C4H4FN2O2)8Pr(SiW11O39)4·10H2O(FPSW) and K26(C4H4FN2O2)8Sm(SiW11O39)4·9H2O(FSSW),were synthesized and their structure were characterized by using elemental analysis,FTIR spectra,X-ray powder diffraction and TG.The antitumor activity tests of the compounds FPSW and FSSW were carried out by the methyl thiazolyl tetrazolium method in hepatocellular carcinoma cell HepG-2.The results showed that FPSW and FSSW could inhibit the HepG-2 cells in vitro significantly.The EC50 of FPSW and FSSW is 1.94×10-5 and 1.32×10-5 mol·L-1 respectively.The therapeutic index of FPSW and FSSW is 0.76 and 1.58 respectively.

Systematic approaches to improving the performance of polyoxometalates in non-aqueous redox flow batteries

Polyoxometalates have been explored as multi-electron active species in both aqueous and non-aqueous redox flow batteries. Although non-aqueous systems in principle offer a wider voltage window for redox flow battery operation, realization of this potential requires a judicious choice of solvent as well as polyoxometalate properties. We demonstrate here the superior performance of N,N-dimethylformamide(DMF)compared to acetonitrile as a solvent for redox flow batteries based on Li3PMo12O40. This compound displays two 1-electron transfers in acetonitrile but can access an extra quasi-reversible 2-electron redox process in DMF. A cell containing 10 mM solution of Li3PMo12O40 in DMF produced a cell voltage of 0.7 V with 2-electron transfers(State of Charge = 60%) and showed a good cyclability. As a means to boost energy density, operation of the redox flow battery at a higher concentration of 0.1 M Li3PMo12O40 produced cells with cell voltage of 0.6 V in acetonitrile and a cell voltage of 1.0 V in DMF;both showed excellent coulombic efficiencies of more than 90% over the course of 30 cycles. Energy density was also increased by employing an asymmetric cell with different polyoxometalates on each side to extend cell voltage.Li6P2W18O62 exhibited 3 quasi-reversible 2-electron transfers in the potential range between-2.05 V and-0.5 V vs. Ag/Ag+. 10 mM Li6P2W18O62/Li3PMo12O40 in DMF produced a cell with cell voltage of 1.3 V involving 4-electron transfers(State of Charge = 50%) with coulombic efficiency of nearly 100% and energy efficiency of nearly 70% throughout the test with more than 20 cycles. These promising results demonstrate proof-of-concept approaches to improving the performance of polyoxometalates in non-aqueous redox flow batteries.

Polyoxometalates for continuous power generation by atmospheric humidity

Atmospheric humidity is a sustainable low-value energy widely existing in natural environment,which is a promising candidate to solve the noncontinuous and low efficiency of low-value energy power generation.Here the mono-substituted Dawson-type polyoxometalates are constructed to be highly dispersed organic ammonium-polyoxoanion clusters and are assembled into thin films power generators with micropores,working in atmospheric humidity.The optimal polyoxometalates generator with the thickness of 7.2μm and the area of 0.36 cm^(2) produces a voltage of 0.68 V and a current density of 19.5μA·cm^(-2) under simulated natural environment,and works continuously and stably under almost all-natural environments(humidity 10%–90%).The highly dispersed polyoxometalate nanoclusters can form microporous in polyoxometalate films to effectively absorb atmospheric humidity and spontaneously form distribution gradient of water,which is the structural basis of power generation.The continuous power generation may be maintained by the effective adsorption and utilization of H_(2)O,the huge electrostatic field of organic ammonium-polyoxoanion clusters,and the reasonably designed polyoxometalates containing inorganic small ions with high mobility.It is the first humidity generator designed with polyoxometalates,which may provide a new research direction for polyoxometalates in sustainable utilization of low-value energy.